Glaucoma is a disease affecting millions of people in the US alone every year. Elevated intraocular pressure (IOP), the most common cause of glaucoma, slowly kills the ganglion cell axons (which collectively form the optic nerve) affecting the peripheral visual field and progressing to the center. If untreated, glaucoma leads to blindness. In general, visual field loss caused by glaucoma is irreversible.
There are a number of external eye pressure measuring devices. Typically, these devices indent the cornea either directly, by contacting it, or indirectly, by a non-contact method (i.e., pneumatic displacement “air puff”), to measure IOP. For example, a Tono-pen manufactured by Medtronic Solan (Jacksonville, Fla.) utilizes micro strain gage technology with battery power and a 1.5 mm transducer tip to gently contact the cornea and display the average of four independent readings along with a statistical coefficient. Both contact and non-contact tonometers are very dependent on the eye wall and corneal rigidity and can be inaccurate because these factors are not taken into account. In addition to the problems of imprecision with many of the external IOP measuring devices, many of these devices, especially those that contact the cornea, can only be administered in physicians' offices.
More reliable IOP measurements can be obtained from within the eye. A variety of devices have been proposed or developed for this purpose.
U.S. Pat. No. 6,579,235 issued on Jun. 17, 2003, the entire contents of which are incorporated herein by reference, discloses a device for passively measuring intraocular pressure of a patient. The device includes an in vivo sensor and an instrument external to the patient for remotely energizing the sensor, thereby permitting the instrument to determine the intraocular pressure. The device directly and continuously measures the intraocular pressure of a patient. The in vivo sensor in the intraocular pressure monitor includes a capacitive pressure sensor and an inductive component. An instrument, external to the patient, measures the pressure, provides readout of the pressure values, and determines the intraocular pressure.
U.S. Pat. No. 6,443,893 issued on Sep. 3, 2002, the entire contents of which are incorporated herein by reference, discloses another device for measuring intraocular pressure. The device includes a remote measuring device adapted to be implanted in an eye. The remote measuring device has a pressure sensor, a converter for converting sensor signals into information for wireless transmission, and a transmitter. The device also includes a receiver adapted to be located outside the eye for receiving information transmitted by the transmitter, and an evaluation device. The evaluation device converts information received from the transmitter into data expressing the intraocular pressure, and records the data. The remote measuring device also includes a data logger in which measurement data continuously supplied by the pressure sensor is stored and from which the measurement data is called up at certain times in operation of the converter.
Patent application Ser. No. 10/686492 filed on Oct. 14, 2003, the entire contents of which are incorporated herein by reference, discloses an optically powered and optically data-transmitting wireless pressure sensor, suitable for implantation in an eye and for monitoring the IOP continuously or on demand. The device may be placed in the anterior chamber of an eye, on the iris of an eye, on an intraocular lens, or on a glaucoma tube.
Most current IOP implants require an external component to receive information regarding the pressure. An optical implant may include a visual indication of IOP, which could be read by an eye care professional by looking into the patient's eye through a magnifying lens system. However, this may require frequent check-ups, which is inconvenient for many patients. Furthermore, several days or weeks may lapse between a change in implant status, such as detection of a high IOP, and the patient's next check-up, and eye or optical nerve damage may occur during this time.
While a conventional digital camera may be used to take a picture of an eye, both the tele-zoom and macro-mode (for shooting images up close, usually from a distance of about 20 cm) functions are insufficient for imaging an intraocular sensor.